1. Field of the Invention
The present invention relates generally to an apparatus and method for preventing frequent handoffs in radio environments with a mixture of a plurality of heterogeneous wireless networks, and in particular, to an apparatus and method for providing a data service to a Mobile Station (MS) concurrently through a plurality of heterogeneous networks.
2. Description of the Related Art
Commercialization of a fourth-generation (4G) communication system is expected around 2010. Research ongoing to provide a stationary data service with a data rate of 1 Gbps and a mobile data service with a data rate of at least 100 Mbps in the 4G communication system. Evolved 2G/3G technologies or many new technologies are provided as technology candidates for the 4G communication system. These technologies provide voice call services as well as high-rate data services that are based on different service concepts. However, presently, there is no breakthrough technology that can be fully qualified as 4G technologies. According to the existing papers and documents, the 4G technology candidates can be classified into the following three groups.
The first group includes Wideband Code Division Multiple Access (WCDMA) and High-Speed Downlink Packet Access (HSDPA) that have been provided by a third Generation Partnership Project (3GPP), and also includes Code Division Multiple Access 2000 (CDMA2000), Evolution for Data Only (1×EVDO), and Evolution for Data and Voice (1×EVDV) that have been provided by a third Generation Partnership Project 2 (3GPP2). These technologies provide an average data rate of only several Mbps, but can support a seamless voice/data service whether under conditions of high-speed movement and can provide a communication service in almost all areas because of its large cell coverage.
The second group includes Wireless Metropolitan Area Network (WMAN) that will be provided as a metropolitan data service by American Institute of Electrical Electronics Engineers (IEEE) 802.16. The WMAN service is also called “802.16 service”. The WMAN corresponds to Korean WiBro, standardized in 2005, and to Intel WiMAX. The WMAN is similar in concept to the existing cellular network, but can support an average data rate of up to several tens of Mbps. The WMAN supports a medium-speed mobility of up to 60 km/h and provides a cell coverage of up to 1 km.
The third group includes Wireless Local Area Network (WLAN) that American IEEE 802.11 developed to replace the existing wired Internet service. The WLAN was standardized in 1999, and has evolved through IEEE 802.11a/b to IEEE 802.11g. The WLAN is now in commercial use and is constantly evolving. Presently, the WLAN provides an average data rate of several tens of Mbps, but is expected to provide an average data rate of up to several hundreds of Mbps in the near future. The WLAN is expected to be the first of the 4G technology candidates that can implement a stationary data rate of 1 Gbps. However, the WLAN hardly supports the mobility and thus merely provides a local communication service with a cell coverage of up to 100 m.
Another candidate for the 4G technologies is an IEEE 802.15 service called “Wireless Personal Area Network (WPAN) service”. The WPAN service has a much larger cell coverage than the WLAN service and supports a data service with a data rate of at least 1 Gbps. For example, the WPAN service is implemented using near-field high-speed communication technologies such as Ultra-Wideband (UWB) technology and Bluetooth® technology. Hereinafter, WLAN and WPAN will be collectively referred to as “WLAN”.
FIG. 1 is a diagram illustrating a radio access environment with a mixture of a plurality of heterogeneous networks.
Referring to FIG. 1, a network 111 (shown as a circle with a solid line) with the largest cell coverage denotes the 2G/3G cellular network, a network 112 (shown as circle with broken lines) with the medium-sized cell coverage denotes the WMAN, and a network 113 (shown as a circle with dashed lines) with the smallest cell coverage denotes the WLAN. It is assumed that a Mobile Station (MS) 103 can receive all services of the above mentioned networks.
The MS 101 in a region 111 can connect and communicate with the cellular network. The MS 123 in a regions 111 and 112 can connect and communicate with the cellular network and the WMAN. The MS 103 in regions 111, 112, and 113 can connect and communicate with the cellular network, the WMAN, and the MLAN. The MS 103 in a given region performs a switching operation through one of a vertical handoff and radio reconfiguration to select only one of the networks that has the best performance in the given region.
However, when the MS 103 selects only one of the networks, the following problems occur.
Firstly, when the MS 103 moves at high speed, a handoff occurs too frequently. As a result, an exchange of control information between the different networks occurs too frequently, which may lead to an overhead against high-rate data communication.
Secondly, when the MS 103 connecting to one of the WLAN and the WMAN moves at a high speed that is unsupportable in the WMAN and the WLAN, an ongoing transmission/reception (TX/RX) operation is not smooth and thus an ongoing communication is broken. In this case, the MS 103 reconnects to the cellular network that can support the high-speed movement, which can lead to another overhead.